The present invention relates to a gear mechanism for a twin screw extruder having two screw shafts that are disposed at an angle to one another.
Drive solutions for double screw extruders are characterized in the process portion, along the drive line, by the characteristic construction, beginning with a motor, a coupling, a gear drive that is to be reduced, a distribution gearbox and the extruder shafts that are coupled on. In this connection, a reduction gearbox converts not only the torque but the speed of the drive source, which is generally embodied as an electric motor. Subsequently, the distribution gearbox simultaneously distributes the drive power, up to now without further change, at a gear ratio of i=1, to both output shafts.
A gear mechanism is known from DE 34 20 918 A1, where two conical, oppositely directed extruder screws are fixedly connected with the output shafts of an extruder gear mechanism. To connect the parallel gear mechanism axes with the crossing axes of the process portion, a universal joint is placed in an output line behind the distribution gearbox. In the main line, the distribution gearbox conveys the first half of the drive power, without changes, into the first extruder shaft. The gear mechanism stage to the second output shaft reverses only the direction of the rotational movement. A change of the mechanical parameters speed and moment does not take place due to the gear ratio i=1. Particularly problematic for the operational reliability of the known gear mechanism are the two parallel herringboned gear sets in one stage.
EP 1 008 437 A1 describes a gear mechanism for a conical gear screw extruder. Depending upon the embodiment, the output shafts rotate in the same or opposite directions. The drive means is characterized by the special, double toothed couplings, which are to be made very small. In this way, it is possible to realize the essential requirement of this double shaft gear mechanism with regard to a very large torque that is to be transmitted, and a very small axial spacing of the screw shafts. The coupling halves of the double toothed couplings have different diameters at their ends in order to achieve an inclined positioning in a very short length.
In the handbook of Plastic Extrusion Technology, Vol. 1, Fundamentals, C. Hauser Publishers, 1989, page 518, various concepts are disclosed for distribution gearboxes in twin screw machines. The types differ from one another by the number of shafts of the distribution gearbox. Gear mechanism concepts can be used having a shaft number between 2 to 5. Depending upon the axial auxiliary forces from the process portion, the prescribed axial spacing of the output shafts, and the torques that are to be transferred, these solutions offer, with regard to the respective application, possibilities for integrating the required large thrust bearings in the housing, or realizing via the power branching a specific tooth loading adapted to the tooth geometry. The important thing with all of the concepts is that no conversions are effected in the line of the main shaft, and gear ratio changes, including the required immediate reversal, are manifested only on the auxiliary branch.
It is an object of the present invention to embody a gear mechanism of the aforementioned general type in such a way that requirements for a compact and reliably operating drive mechanism are fulfilled, and in particular by means of a straightforward structural assembly with components designed in a special manner towards this end, preferably for the upper power or capacity range.